I have decided to get back to running about 3 times a week, how long should I run for so that the muscle loss is kept at a minimum? 20 minutes?

20-30 minutes of normal cardio

but

i'd suggest you go for HIIT type cardio, best at burning fat while avoiding muscle loss

both

2-3 times a week of cardio is sufficient.

agreed. do cardio for your heart and lung capacity...don't try to burn fat with cardio. doesn't really work that way.

I probably will do 25 minutes of cardio, I heard that doing more than that will burn muscle too and I dont want that lol.

Are you suggesting that HIIT cardio is an ineffective way to burn fat?

Malkore is a little off here.....Fat only burns in the presence of oxygen.....so yes cardio will burn fat.....however it is a double edged sword.....it shows no prejudice towards other sources of calories like muscle.
People use circuit training to attempt this effect with weights.....but unless you are able to continue moving that weight for more than 3 minutes.....it ain't gonna happen.
I agree with Joey....learn how to properly do HIIT. HIIT is very shortlived cardio/anaerobic training....go past 10 minutes and most likely you are not really giving it maximal effort. Also do cardio in long duration form....say 75% heart rate....try it for 10-30 minutes.

Never underestimate the power of a high RMR.

If you put a Honda civic and Lamborgini Diablo at a stop light (in idle) for 1 hour .....which burns more fuel?
The Diablo!!! The honda civic is too efficient at burning fuel....but that diablo......DAMMM....
This is just like the human body a person with a bigger engine (RMR-more muscle) will burn a lot more of calories just looking at the weights than a "cardio bunny" on a cellphone operating the treadmill.

I was too general. But my main point was, don't try to use cardio as your mechanism to burn the fat. Too many people get wrapped up in the 'more cardio = skinnier body' mentality, and as Trainerty clarified, you can just as easily take down muscle with the fat, and that's counter productive if you wanna burn calories like the Lamborgini.

Cardio is a good thing, but if you think you have to exceed 30-40 mins per session to get anywhere...you're stuck in the wrong mindset.

yes, of course DIETING is the main factor to losing fat/weight, but with cardio and weight resistance, people tend to lose weight faster than dieting alone.

Malkore i've to disagree with your "claim" that cardio will not help burn fat. as you may or may not already know. High Intensity Inteveral Training is the best type of cardio to burn off fat, if you wish to learn more about it, search the forum :] , but anyways, the difference between HIIT cardio and regular cardio is that, during HIIT cardio, you attempt to keep your heart rate 90-100% the time when your sprinting, and while ur not sprinting, your heart rate drops down to 60-70%, which would be joggin, etc. In regular cardio you are "constantly" keeping you heart rate at 70-80%, which is not bad, but the problem with regular cardio is, there is probability of muscle loss, not only burning the extra calories. HIIT is different as your body initiates hormones that utilizes the body's fat storage as fuel. HIIT is best with an empty stomach.

:::HIIT cardio , 10-20 minutes is sufficient enough, most personal trainers advise their clients to do 10 minutes, 30 seconds @ 90-100% heart rate , then jog/walk for 45-1 minute. Minimal muscle loss. 2-3 times a week is enough, unnecessary to attempt regular cardio while in a HIIT program.

yes its true, lots of obese individuals use cardio, along with proper dieting and workout, burn off those pounds of fat right off and as a note to anyone: 3500 calories = 1 lb. Cardio is the one of the essential parts to cutting, imo. and experience.

Last of all Malkore, i think you have mistakened HIIT to regular cardio, get it straight :]